title: Mechanism of sodium uptake in PNA negative MR cells from rainbow trout, Oncorhynchus mykiss as revealed by silver and copper inhibition.
abstract: The rate of acid-stimulated and phenamil-sensitive sodium (Na(+)) uptake was measured in three different cell lineages: pavement cells (PVC), total mitochondrion-rich (MR) cell populations, and peanut lectin agglutinin-negative mitochondrion-rich cells (PNA(-) MR) isolated from the rainbow trout gill epithelium. Despite the presence of basal levels of Na(+) uptake in PVC, this transport was not enhanced by acidification, nor was it inhibited by independent treatment with bafilomycin (i.e., a V-type H(+)-ATPase inhibitor), phenamil (i.e., a specific inhibitor of ENaC), or Ag (a specific inhibitor of active Na(+) transport in fish). In contrast, Na(+) uptake in PNA(-) MR cells was increased by ~220% above basal levels following acidification of near 0.4 pH units in the presence of 1.0 mM external Na(+). Acid-stimulated Na(+) transport was entirely inhibited by both phenamil and bafilomycin. Silver (Ag) and copper (Cu), which are known to interfere with active Na(+) transport in fish, were also responsible for inhibiting acid stimulated Na(+) uptake in PNA(-) MR cells, but by themselves had no effect on basal Na(+) transport. Thus, we demonstrate that Ag specifically prevented acid-stimulated Na(+) uptake in PNA(-) MR cells in a dose-dependent manner. We also demonstrate rapid (<1 min) and significant inhibition of carbonic anhydrase (CA) by Ag in PNA(-) MR cells, but not in PVC. These data lend further support to the idea of a PNA(-) MR cell type as the primary site for Na(+) uptake in the freshwater (FW) gill phenotype of rainbow trout. Moreover, these findings provide support for the importance of intracellular protons in regulating the movement of Na(+) across the apical surface of the fish gill.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6E 4W1. greg.goss@ualberta.ca
authors.forename: Greg
authors.initials: G
authors.lastname: Goss
authors.forename: Kathleen
authors.initials: K
authors.lastname: Gilmour
authors.forename: Guy
authors.initials: G
authors.lastname: Hawkings
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Brumbach
authors.forename: Maily
authors.initials: M
authors.lastname: Huynh
authors.forename: Fernando
authors.initials: F
authors.lastname: Galvez
mesh_terms: D000818:Animals; D002256:Carbonic Anhydrases / Q000378:metabolism; D003300:Copper / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D020135:Peptide Nucleic Acids / Q000378:metabolism*; D012834:Silver / Q000494:pharmacology*; D012964:Sodium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D018942:Macrolides; D020135:Peptide Nucleic Acids; C057620:bafilomycin A; D012834:Silver; D003300:Copper; D012964:Sodium; D002256:Carbonic Anhydrases; D000254:Sodium-Potassium-Exchanging ATPase